-LRB- CNN -RRB- -- The man leading the hunt for Malaysia Airlines Flight 370 says the search is the most difficult in human history , but modern technology greatly increases the chances of finding the missing plane .

The four underwater signals that search teams detected are still `` the most promising lead '' investigators have in the search for the Boeing 777 , Angus Houston told CNN 's Anna Coren on Monday .

But are they all pings from the plane 's data recorders ?

A Wall Street Journal report Monday said authorities increasingly believe only the first two signals detected are relevant to the search . And a U.S. Navy source told CNN that Navy officials assisting in the search are sharing the signal data with U.S. agencies and consultants for `` re-analysis , '' adding that searchers have more confidence in the first two pings detected .

Houston told CNN it 's still too soon to rule out any of the signals .

`` Analysis on all four detections is continuing , '' he said . `` At this point in time , it is too early to discount any of the acoustic detections . ''

The pings have played a key role in shaping the search for the plane , which went missing March 8 during a flight from Kuala Lumpur to Beijing with 239 people onboard .

Houston told CNN the hunt for the plane is even more difficult than that for Air France Flight 447 , which disappeared in the Atlantic Ocean in 2009 .

`` The big difference between Air France 447 and MH370 is that the last known position , in terms of MH370 , is at the top of the Malacca Straits , and then the aircraft continued to fly for an extended period after that , '' Houston told CNN 's Anna Coren on Monday .

`` Whereas Air France , they had a very good last known position , which then turned out to be very close to where the aircraft was eventually found . ''

But he said searchers are performing `` groundbreaking work '' with satellite analysis , which has helped isolate the search area in the Indian Ocean .

`` Without that , we would be essentially searching the whole of the Indian Ocean , and I think the chances of finding the aircraft in those circumstances would have been slim , '' Houston said . `` I think by having this defined search area ... I think eventually we will find the aircraft . ''

Houston is the chief search coordinator for the Joint Agency Coordination Centre , based in Australia . He said his greatest concern throughout the two-month search has been the families of those on board .

`` To have a set of circumstances where you do n't know what 's happened to your loved ones in circumstances such as this , it 's just a terrible , terrible emotional trauma of all of those involved , '' he said .

`` And beyond that , the wider public has a great interest in what happened here because we all fly in airplanes , and we all fly long distances over water , and a lot of people want to know what happened and why it happened . ''

Hunt for MH370 gets deeper , broader , pricier

About criticism of Malaysia

Since the plane disappeared on March 8 with 239 people on board , the Malaysian government has been criticized for its response and accusations that it has not been transparent .

Houston said he believes Malaysia has been forthcoming .

`` I think some of the commentary about what the Malaysians have done , I do n't think is as fair and objective as it might have been , '' Houston said . `` People are looking for answers , and there are no answers at the moment . That 's the difficulty . ''

` It just disappeared '

Houston said he understands why many families are frustrated by the lack of information .

`` Initially , the aircraft -- well , simply put , it just disappeared . And I guess in this day and age , that surprised a lot of people , '' he said .

But such a disappearance is quite possible if the transponder or anything on the aircraft that transmits signals is turned off .

`` I think that 's something that we , as a world community , have to correct as soon as possible , '' Houston said . `` We need to have jetliners that are equipped with some sort of tracking device that ca n't be turned off , that can be tracked all of the time . And with satellite technology available , I think that can be done in the near future . ''

On the same day that Houston spoke , a satellite communications company said it would begin providing a free global airline tracking service .

Inmarsat , the company whose satellite had the last known contact with Flight 370 , said it proposed the service to the International Civil Aviation Organization ahead of the ICAO 's conference on aircraft tracking this week .

`` This service is being offered to all 11,000 commercial passenger aircraft , which are already equipped with an Inmarsat satellite connection , '' the company said in a statement .

It said the tracking would cover `` virtually 100 % of the world 's long haul commercial fleet . ''

CNN 's Rene Marsh and Catherine E. Shoichet contributed to this report .

@highlight

NEW : Angus Houston says underwater signals remain `` the most promising lead ''

@highlight

`` Groundbreaking work '' with satellite analysis will help find the plane , he says

@highlight

Houston defends Malaysia 's response to the missing plane

@highlight

Inmarsat offers free global airline tracking to all 11,000 commercial passenger planes